The present invention relates to a type of pressure transducer including a sensing element mounted on a substrate where the pressure of a fluid is transferred to the ceramic sensing element by a flexible media isolating material such as a medical grade media isolating soft gel, typically polydimethylsiloxane or similar.
One prior art transducer of this type is illustrated in FIG. 4 this transducer includes a housing 400 with a fluid channel 402 extending across one outer side. The fluid channel is terminated with lure connectors or similar (not shown) for connecting a fluid transmission line to each end. In use the fluid for which the pressure is to be monitored occupies this channel. The housing includes a cavity 404 facing away from this channel. A dividing wall 480 separates the channel 402 from the cavity 404. A small upstand wall 408 is formed on the inner face of the cavity 404 around an aperture 406. The upstand wall 408 is spaced a small distance away from the aperture 406 to leave a narrow internal flange. A foamed polymer gasket 410 sits within the cavity 404 against the dividing wall 480. The gasket 410 has an aperture 420 fitting over and around the upstand wall 408. The gasket includes a raised pad. An array of linear conductors 424 is fixed to the top of the pad. A sensor component sits in the cavity against the foam gasket. The sensor component includes a silicon wafer substrate 430 carrying sensing element 432 and associated electrical and electronic circuitry. A resilient O-ring 428 is bonded to one side of the substrate 430. A rigid cap 426 is bonded to the other side of the wafer covering the sensing element 432. A small hole 440 in the centre of the cap allows pressure equalisation in the enclosed space. A media isolating gel 442 fills the central opening of the O-ring 428 down to the sensing element. The sensing component is located in the cavity 404 with the O-ring 428 located within the upstand wall 408 and compressed against the internal flange. This provides for a seal at the O-ring, while fluid in the channel may pass through the aperture and press against the exposed area of the isolating gel 442. Electrical contacts on the substrate 430 contact disparate groups of the array of electrical contacts 424 on the gasket. A cable component 450 is terminated at one end with a receiver component 452 that fits within the cavity 404. A pair of clips along each side of the receiver body interact with complementary clips of the housing 404 to hold the receiver body in place within the cavity. The receiver includes a recess 454 on the side facing the dividing wall 480. The sensing component fits within this recess with the O-ring 428 protruding. The base surface 456 of the recess presses against the outward face of the rigid cap, but the hole through the cap is in registration with an extension 464 of the recess. The receiver includes electrical contacts 460 extending from electrical conductors in the cable end 462 encapsulated by the receiver body. The electrical contacts 460 press against disparate groups of the array of conductors 424 on the raised pad of the gasket. These disparate groups at least roughly correspond with the same disparate groups that are in contact with the sensor component contacts to complete an electrical connection between the sensor contacts and receiver contacts. In this transducer design the soft gel isolating material is contained by the flexible O-ring. The inventor of the present invention has determined that this is a source of potential error.
Another prior art pressure transducer is described in U.S. Pat. No. 5,540,100. This is another example of a pressure transducer that includes a pressure measuring element on a ceramic substrate. The element is provided to be in fluid communication with a fluid channel. In this prior art design the sensing element and substrate are not isolated from the fluid in channel.